1. Field of Invention
The present invention relates a semiconductor process. More particularly, the present invention relates to a method for stabilizing an etching performance.
2. Description of Related Art
With the development of the advanced semiconductor processes, such as 90 nm CMOS processes, the size of the pattern is getting smaller and smaller. Dry etching is an etching technique that bases on the principle of particle bombardment to perform thin film etching. Plasma etching is a type of dry etching, wherein the reacting gas molecule is ionized by plasma to form ions that are reactive with the thin film material. The thin film, after being exposed to plasma, is converted to a volatile product due to the chemical interaction between the ions and the thin film. The volatile product is then removed to complete the etching process.
Currently, the plasma used in the etching process is often generated from a halogen containing gas mixture, which includes carbon tetrafluoride (CF4). C4F8, C5F8 or C4F6 are also being used as reacting gas to provide carbon atoms and fluorine atoms. However, by using this kind of plasma in the etching process, polymer byproduct composed of carbon, fluorine, nitrogen and oxygen elements, is formed in the pattern of the etched material layer and on the wall of the etching chamber when the etching process is completed. In general, the aforementioned polymer byproduct becomes the factor affecting the etching environment within the etching chamber and affecting the performance of the etching process in the posterior etching process step. That is, the endpoint detection is interfered and the interference factor leads to endpoint mis-catch. Therefore, the target layer is etched through and the material layer under the target layer is damaged.